Light emitting diodes, or more commonly known as LEDs are gaining popularity for solid-state lighting. In the field of solid-state lighting, most of the light sources are white light.
Color rendering index (referred hereinafter as “CRI”) is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. The International Commission on Illumination defines CRI as an effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant. Usually, light sources with a high CRI are desirable in color critical applications such as photography and cinematography. In the field of Solid State Lighting, light sources with higher CRI are more desirable because objects under light sources with high CRI may appear more natural to users.
On the other hand, the color temperature of a light source may be defined as the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source. The color temperature of a light source indicates the relative color appearance of the particular light source on a scale from “warmer” (more yellow/amber) to “cooler” (more blue) light. Color temperatures are generally given in Kelvin or K. Color temperatures over 5,000K are called cool colors (bluish white), while lower color temperatures (2,700-3,000 K) are called warm colors (yellowish white through red). Choices of color temperatures may depend on a user's taste or personal choice, and may differ from one person to another.
From manufacturing perspective, supplying light sources having different color temperatures and different CRI may be challenging. Typically binning may be required. In addition, the end products of any light sources may need to be divided into multiple classification or category that makes manufacturing less cost effective and complicated.